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debuggingsmalltalkpharo

Change the way an object is displayed in debugger/inspector variable-value table

I would like to know if there is a message I can override in Pharo so that my custom classes display more descriptive information in the inspector/debuger much like simple variable types do, like Integers or Strings. For instance:

enter image description here

Instead of that, I would like it to show a more custom and informative description consisting of its internal variales so as to have a tighter/tidier view of the variables instead of having to click on it and open another chart (therefore losing sight of the information on the previous chart). I know you can increase the amount of charts shown below, but that is not the point of the question. I would like to achieve something like this:

enter image description here

I have browsed the pharo forums and found nothing, I have also tried overriding over 30 methods hoping that one of them changed the output. Only the class message seemed to change the output, but I could only return an instance of Metaclass and besides messing with this message would break a lot of stuff. Finally I tried to reverse engineer the debugger and then the inspector to see at which point is the table constructed and what values are used or which messages are sent to build said values, but it was just too much for me, the callstack kept growing and I couldn't even scratch the surface.

Solution

  • Luckily, doing this in any Smalltalk is very easy. Types inherited from Object are expected to answer to the message printString, and ultimately printOn: aStream. Those messages are expected to give a description of the object. So, you should just override printOn: in your class (printString uses printOn:) and all the browsers and inspectors will automatically use it. There other possibilities in Pharo, if you want to provide more complex information in different tabs, but I think printOn: will suffice for you.

    An example would be:

    MyPoint>>printOn: aStream
    aStream nextPut: ${.
    x printOn: aStream.
    aStream nextPutAll: ', '
    y printOn: aStream.
    aStream nextPut: $}